An air conditioning apparatus is provided that can individually arbitrarily perform cooling and heating operations. (For example, refer to Patent Document 1) In such an air conditioning apparatus, a refrigerant flows in the same direction in a plurality of refrigerant piping from a heat source apparatus to a plurality of indoor units (load side units). That is, a high-pressure refrigerant is output from the heat source apparatus and a low-pressure refrigerant returns to the heat source apparatus. Thereby, there is one heat source apparatus and since the refrigerant returns to the heat source apparatus always through a single piping from a plurality of indoor units, the refrigerant returns to the heat source apparatus in the proper quantity. In addition, hereinafter high or low pressure is not specified in relation to a reference pressure but represented as a relative pressure by such as pressurization by a compressor 11 and a refrigerator pass control by each throttle device. Further, it is the same for high and low temperatures.
The refrigerant oil discharged from the compressor in the heat source apparatus returns through the indoor unit to the heat source apparatus, however, since such refrigerator oil all returns to a single heat source apparatus, problems such as a depletion of the refrigerator oil hardly occur.    [Patent Document 1] Japanese Examined Patent Application No. H7-52045